The present invention relates to a variable mirror capable of varying the configuration of a reflecting mirror to change the reflecting direction of light.
Another invention in the present invention relates to an optical apparatus including a variable-optical-characteristic optical element, a variable-optical-characteristic mirror, or a combination thereof.
Still another invention in the present invention relates to an optical system using the above-described variable mirror, etc. More particularly, the invention relates to an optical system capable of focusing, etc. for a camera, a video camera, a digital camera, a finder, a viewing optical system, an image display device, and so forth.
This type of variable mirror is widely known, for example, from Japanese Patent Application Unexamined Publication (KOKAI) No. 5-157903. A variable mirror described in this publication is produced in a very small size by making use of a semiconductor manufacturing technique with a view to using the variable mirror in a micromachine. The variable mirror has a mirror body formed from a sheet 1 of single crystal silicon. As shown in part (A) of FIG. 80, the sheet 1 includes a thin inner portion 11 and a thick outer peripheral frame portion 12 surrounding the inner portion 11. The sheet 1 is supported at the outer peripheral frame portion 12 by a thick outer peripheral frame portion 13a of a glass substrate 13, which is a support member. The glass substrate 13 has a thin inner portion 13b surrounded by the outer peripheral frame portion 13a. A space is created between the inner portion 13b of the glass substrate 13 and the inner portion 11 of the sheet 1. An electrode film 13c is formed on the upper surface of the inner portion 13b of the glass substrate 13.
An upper surface 11a of the inner portion 11 of the sheet 1 is a flat mirror-finished surface, and a lower surface 11b thereof is a flat finished surface, although it is not a mirror surface.
In the conventional variable mirror arranged as stated above, when a voltage is applied between the sheet 1 and the electrode film 13c, electrostatic attraction occurs therebetween, causing the inner portion 11 of the sheet 1 to curve so as to be convex toward the electrode film 13c. Consequently, the upper surface 11a forms a concave mirror. The degree of curvature of the inner portion 11 can be changed according to the magnitude of the above-described voltage. Accordingly, by changing the magnitude of the voltage, the position of the focus F of the concave mirror, which is formed by the upper surface 11a, can be moved along an optical axis O of the concave mirror.
However, the conventional variable mirror, in which the inner portion 11 is formed with a uniform thickness as stated above, suffers from the problem that the curved inner portion 11 is a biquadratic surface and therefore the concave mirror of the upper surface 11a produces unfavorably large aberrations.
To solve the problem, Japanese Patent Application Unexamined Publication (KOKAI) No. 5-157903 proposes an arrangement such as that shown in part (B) of FIG. 80. In this arrangement, the lower surface 11b′ of the inner portion 11 of the sheet 1 is not flat but formed from a plurality of curved surfaces. More specifically, the lower surface 11b′ is constructed by forming different curved surfaces concentrically. The central portion of the lower surface 11b′ is formed from a paraboloid A. A peripheral portion surrounding the central portion of the lower surface 11b′ is formed from a cubic surface B. Because the lower surface 11b′ is formed by combining together a plurality of curved surfaces, when the inner portion 11 is curved by electrostatic attraction as stated above, the upper surface 11a becomes a concave mirror formed from a paraboloid (quadratic surface). Accordingly, large aberrations are not produced.
The configuration of the lower surface 11b′ shown in part (B) of FIG. 80 is determined by a mathematical expression. The lower surface 11b′ is formed by laser-assisted etching. However, as the external size of the variable mirror decreases, it becomes more difficult to form the lower surface 11b′ into such a complicated configuration with high accuracy [particularly within λ (wavelength of light)/n (n is generally a value of about 10), which is optical tolerances required]. In addition, it is desired to allow the mirror surface to be changed into even more various configurations other than the paraboloid (quadratic surface), as desired, so that the mirror surface can be applied to various optical systems.
Moreover, large electric power is needed to increase the degree of curvature of the inner portion 11 in the above-described conventional variable mirror, in which the inner portion 11 of the sheet 1 is curved so as to be convex toward the electrode film 13c by utilizing electrostatic attraction, thereby forming the upper surface 11a into a concave mirror.
Conventionally, a digital camera is built by assembling together components as shown in FIG. 81, i.e. a plastic lens PL, a diaphragm D, a focusing solenoid FS, a shutter S, a charge-coupled solid-state image pickup device (CCD), a signal processing circuit PC, and a memory M.
Incidentally, the image-forming performance of plastic lenses generally degrades with changes in temperature because the refractive index and configuration thereof change with changes in temperature and humidity. Therefore, glass lenses are mostly used. For this reason, there are limits to the achievement of a reduction in weight, increase in accuracy and reduction in cost of products.
There has heretofore been known a prism optical system formed by combining a free-form surface and a prism with an optical system of a digital camera or the like as disclosed, for example, in Japanese Patent Application Unexamined Publication (KOKAI) Nos. 9-211330 and 9-211331. In these prior art references, however, no mention is made of a method of focusing for each object position.
Focusing of such a prism optical system is mentioned in part in Japanese Patent Application Unexamined Publication (KOKAI) No. 10-6886. However, what is mentioned therein is a focusing mechanism in which focusing is performed by moving a prism or an image plane along an optical axis as in the case of a coaxial system.
Meanwhile, there has heretofore been an adaptive optics technique in which the disturbance of the wavefront caused by atmospheric fluctuation is corrected by inserting a variable mirror in an optical system of a telescope [e.g. “Applied Physics”, Vol. 61, No. 6 (1992), pp. 608–611].
Regarding a focusing system for focusing or diopter adjustment in a reflecting optical system using a rotationally asymmetric surface, because the optical system is a decentered optical system using a rotationally asymmetric surface, if focusing is effected with a lens frame-rotating mechanism similar to that used for a coaxial system, when the rotationally asymmetric optical system rotates together with the lens frame, the image also rotates undesirably. To prevent this, it is necessary to change the distance to the image plane without rotating the rotationally asymmetric optical system. The scheme for preventing the rotation of the image causes the number of components to increase and results in an increase in size of the apparatus, unfavorably.
In the case of aiming principally at mass-production of the decentered reflecting optical system using a rotationally asymmetric surface, it is common practice to employ a technique of production by molding. In the production by molding, however, significant errors are introduced into optical parts produced, causing the optical performance to be degraded.
Although the following matter is not limitative to the decentered reflecting optical system using a rotationally asymmetric surface, the refractive index and configuration of optical parts generally change according to environmental conditions, e.g. temperature and humidity, causing the optical performance to be degraded.
In a zoom optical system, it is impossible to actively change the condition of aberration that varies with the change of the zoomed condition.